Neutral-to-polar current conversion circuits



Mwah mi, 1956 J. s. HARRIS 21,779,677

NEUTRAL-TO-POLAR CURRENT CONVERSION CIRCUITS Filed April 29, 1952 v3Sheets-Sheet l www 2 @gjm 3 1 www 5 mm@ ffl? l; 2 s 1 2/f) W2 WM@ ow/wmim 5@ AMM caw/mw 3j INVENTOR JAM/55 5 HAHN/5 BY N AT ORNEY Mmm, 13 1956J, S. HARRIS NEUTRALTOPOLAR CURRENT CONVERSION CIRCUITS Filed April 29,1952 5 Sheets-She et 2 KE Y//V INI/ENTOR.

JAMES 5 #ARH/,S

BYMMW/lm /TTORNEY mmh 13, 195

J. S. HARRIS NEUTRAL-TO-POLAR CURRENT CONVERSION CIRCUITS www. 3l u wwwAVH/nm 162 1; /A/M/r l Pam@ @www www WE ENVENTOR JAMES, .5'. HA ,LW/5

ATTORNEY Unite rates Patent NEUTRAL-T-POLAR CURRENT CONVERSION CIRCUITS.lames Stallings Harris, Old Greenwich, Conn., assignor to RadioCorporation of America, a corporation of Delaware Application April 29,1952, Serial No. 284,863

S Claims. (Cl. 178-70) The invention relates to telegraph signal-lingcircuits. It particularly pertains to circuit arrangements forconverting signal currents appearing in neutral form into signalcurrents of polar form.

Fundamentally in any telegraph signalling circuit intelligence istransferred by means of switching the transmission line input terminalsto effect a change in the current conditions of the circuit. A familiarexample of such a circuit is a D.-C. telegraph circuit employingprinting telegraph equipment in which the signal is actually detected bya magnetically operated armature in the receiving printer. In order forthe receiving equipment to properly interpret the intelligencetransmitted, it is essential that the position of the armature of thereceiving printer accurately follow the keying device at the remotetransmitter. That is to say, that the duration between transitions ofthe armature should be the same as the duration between transitions ofthe contacts of the keyer. Assuming that the wave filter characteristicsof the transmission line are satisfactory, the adjustment of the circuitwhich will satisfy the requirement as mentioned above is largely amatter of adjusting the power supply voltage and total circuitresistance to provide a specified current in the armature coil duringsteady-state marking condition. In usual practice the power supplyvoltage is xed so the adjustment is actually an adjustment of resistancein the circuit. Because the transmission line impedance is usuallyfixed, such adjustment may be made only at the ends of the transmissionline.

As is well known to those familiar with the telegraph art, such acircuit works satisfactorily only so long as the transmission lineimpedance actually is a xed quantity, and any changes in this impedancerequires compensation at one or both of the terminal ends of the line ifoperating tolerances are to be maintained.

In the case `of long ltransmission lines the current at .the load end ofthe circuit. will vary due to changes in both humidity and temperature.Such changes do oc- 4cur `relatively slowly as compared with the speedof changes due to the intelligence keying impressed upon the line, butthe circuits require periodic readjustmcnt to maintain adequatetolerances.

In order to eliminate the requirement for these readjustments due tochanges in line characteristics, which may be considered as changes inline attenuation, it is almost universal practice to use a differentcircuit on long lines. This circuit is known as the two-current or polarcircuit.

In the two-current circuit the mark and space currents are identical inmagnitude but opposite in polarity. Changes in line attenuation,therefore, alect the magnitudes of the mark and space currents to thesame degree, but have no effect on the polarity component. Ihe prior artsignal detection device in such circuits may be, and usually is, asimple polar relay which responds to a combination of current magnitude`and polarity, the response being effected at a current magnitudedetermined by the physical characteristics of the particular relay.

'ice

In a properly operating circuit, the magnitude of current required forproper operation of the relay in either direction is usually the same.With such a signal detection device it is only necessary to assure thatunder the maxi-mum anticipated line attenuation the current supplied tothe device will not exceed the safe maximum which may be applied to thedevice without damage or misfunction.

There are a large number of existing neutral signal type lines howeverthat do not lend themselves for polar operation and which would requireextensive alterations in order to convert them for polar operation.Obviously such alterations are expensive from both pecuniary and circuittime standpoints.

It is an object of the invention to convert neutral or single signallingcurrent to a form approximating the performance of polar or twosignalling -currents in an improved manner.

It is another object of the invention to provide an improved controlcircuit arrangement for converting neutral or single current signals topolar or two current signals.

A further object of the invention is to provide an improved tone signalconverter and monitoring circuit adaptable for use in a multiplexreceiving installation and including a control circuit arrangement forconverting neutral or single current signals to polar or two currentsignals.

The objects of the invention are attained in a circuit arrangementcomprising three resistive elements, a capacitive element and aswitching element. One of the resistive elements is arranged between theneutral signal input terminals. The lother resistive elements areconnected in series across the capacitive element to form a potentialstoring and dividing network which is connected in series with ltheswitching element across the input terminals. The series arrangementbetween the junction of the series connected resistive elements and theswitching element is connected to -the output terminals of the novelcircuit arrangement. In accordance with the basic principles of theinvention the switching element is arranged to close when, and onlywhen, the signal voltage across the input terminals equals or attemptsto exceed the voltage across the capacitive element.

A current conversion circuit according to the invention may be used tooperate a polar relay directly or through the intermediary of anelectronic amplifier. Alternately a differential amplifier may be drivenby the current con- Version circuit to operate any desired utilizationdevice, Another mode of operation may employ a conversion circuitaccording to the invention for triggering a nonstable or a bistablereciproconductive circuit, sometimes respectively referred to asflip-flop and locking circuits.

By changing the relative values of the series connected resistiveelements zero current space-current mark signals, proportional currentmark-space signals, and double current or opposite polarity mark-spacesignals may be accommodated. Such changes can also be made for thepurpose of reducing distortion present in a received signal orconversely for the purpose of introducing a desired distortion orweighting of the signal.

The invention will be illustrated in connection with specic embodimentsthereof given by way of example only and described with reference to theaccompanying drawing forming a part of the specification and in which:

Figs. l and 2 are diagrammatic representations of telegraph signallingcircuits known to the zart;

Fig. 3 is a schematic diagram of a circuit arrangement basic to theinvention;

Figs. 4 and 5 are functional diagrams useful in excuit 'diagram ofa'known single-'currentelectric "signalling-'f circuit'comprising' atransmission linelto'which a signal detection device 17A and theequivalent loadimpedance 19are connected. kIntelligence .is'tran'sferred'to' the detection' device'17 vlocated atithe receiverV by means' of akeying device 21 located at the transmitter' which switches the inputvterminals Aof the transmission line ".15 to effect a change in thecurrent Vconditions 'of the. circuit. A current source 23 andtheequivalent mark source impedanceiZS are. connected to theline by thekeyingidevicel. 'It is obvious thatthecorresponding space sourceimpedance 27 may be equivalent to an open circuit in which case thekeying 'device 21 may consist of only two contacts in a makend-breakcircuit. `In order for the receiving equipment .to -properly interpretthe intelligence transmitted, it is essential that the signal .detectiondevice :accuratelyfollow the movable contacts ofthe keying .device'ZLlThat is to say that the duration between transitions of the armature ata telegraph printer, for example, should bethe sameas the durationbetween transitions ofthe contact of the keying device 21. 'Assumingthat the waveltercharacteristics of the transmission line 15 aresatisfactory, the adjustment of the circuit which satisfies therequirement as mentioned above is largely a matter of adjusting thevoltage ofthe source, 23 and total circuit resistance to provide aspecified `current through the detection device 17 and the loadimpedance .19 during steadystate marking condition. In usual practicethesource voltageis. iixed so that in practice the adjustment isactuallyan adjustment .of resistance .in the circuit andlis made only at .theends of the transmission line.

`Such a circuit ,will be .satisfactory-as long as` zthetransmission lineimpedance actually isadixed quantity. Any changes in this impedancerequire compensation. ati-one or both of theterminalsinorder..tomaintain `the operating tolerances.

In the case of long transmission 1ines,the two-current or polar circuitshown in Fig. 2 is .employediat the transmitter, the remainder ofthecircuitbeing-as `show-r1` in'Fig. 1.

v-Inthis type-of circuitthe mark and space currents obtained fromthesources 23. and 29- are usually'identical inxmagnitude butaoppositetin.polarity 'and' the-source impedances and ,27 are:likewise..identicalnsonthat changes inline attenu'ation1afect Ithemagnitudes -of the marktand space currentsto-the samefdegnee.

The double-current .circuit isA alsof .valuable under conditions wherethe `signal as-ireceivedfmay 4include-1eX traneous .noise orinterference components: 10ft. a Ymagnitude sufficient to .cause false.operationrof aisingle current device, as they can=bemade-ineffective:in-aftwoacurrent circuit, providedvthey are 4withinthelimitations of 1allowahlemaximum current.

The. preceding information,v repeated'here only" for backgroundpurposes, :isvwell known andtmorewcomplete discussions. may-be Yfound-inthe. literature 1of;;the,. cornmunications art.

. Further, .while the preceding discussionhhas.- assumed a continuousD.C. circuit between the keying deviceiat` the transmitterand the..signal vdetection device attthe receiver, it is. to. be-understood:.that the-circuitntheory of theembodimentto be describedis.not..af`fectedif tcarrier methods are employed on the transmission.linelS with the understanding that `the .actual signaLappliedzat thefinal utilization point (for example, the printer magnet)"is"usually" a"single 'current'signak and `that' 'single frequency on-off A.C.or"keyed tone signals on the transmission line correspond to singlecurrent circuitry, while two frequency or frequency shift signals on thetransmission line correspond .to two-current or polar circuitry. Itshould also be recognized that where the transmission line .includes `a:radio circuity the changes in line attenuation may'berquiterapid.

Referring to Fig. 3 there is vshown in schematic form a basic Circuitarrangement accordingitothe invention,v

tor C. Thefresistance elements RLand R2=may.be..sep.

arate resistors, a single tapped resistonor a potentiometer having avariablertappingarm. Theswitchir 1g.t=,1e

t mentsmay be :anyknown device -will..wi1l,presenta very low. impedanceat the operating .frequency between' the lowerend ofthe shunt network.'SSand-:the ,terminals 32,.and,38. Inaccordance.withrtheinventiom the.switching elements. should. closeI when, and,only when, .therpotential.Y applied .across the 4input terminals,31-f32 equals or.attempts .,to. exceed. the Avoltage-across. the network capacitor C.-This..feature -Will bediscussed--further:.as the'descriptionprogressesThe circuit supplyingffpower to the neutral'input ',ter-

' minals 3.1-32 should-preferably be relatively ylow `in impedance ascomparedytothesum of resistanceszofthe network .resistors R1 and l:R2andshould alsogpreferfably supply A.current-and voltage-during the fidle,-,condi.- tion.

long v.with .respect to ther anticipated. E maximum continuf ousspacinginterval.

Under these conditions,l :the 5schematic i'rrepresentation of Figs. 4andfS illustrate rthezmanner inrwhich the .circuit functions. :The.capacitorIC. is: chargedztoithe 'steady state markvoltage:.Esgthroughtthe 'switching element S andtheA relatively low.effecti've resistanceofthe .source resistor: R5 andnzthe' resistance.element R3, Iwhile (the: dist charge path is 'the series connection`ofitheresistorsRl and'RZ. ,Infthe space 'condition the :resistanceyelement R3 .serves to. reduce the r potential' `between .the neutralinput terminals? 31+32to :zero whenithe current-source T18 is zremoved.As .'shownrin the: twot-Figs. 4 and`\5, #the output voltages for the-two conditions areasifollows:

Input Output :.E. VOl'S vRg SR1-PE2 Space=Zero Volts E "R1 *Riem Thusthe voltage between the output.terminals"3738 reverses in polarity forthe *two conditions. "The total magnitude of change'inithe outputvoltage isequal to the magnitude of' the input voltage under mark.condition..and the relative magnitude of the markl and space voltagesis determined by the relative rsistances of the two resistors 'R1and`R2. "Thus'ifthe resistance values of. the resistors R1 andQRZareequal, theoutput voltage will be ai. balanced polar voltage,`while'if 'the values are .unequaLhe output will` be antun'b'alanced.

polar voltage` with the'degree of voltageunbalanceequal to'the` degreeof resistance unbalance.

'While .the actual transmission .line .hetweenterminals still remains: a.neutralsignal,:1ine,..the circuit farrauge- That is, mark :is thesteadyistateidle condition, while. the fspace or no current conditionappears; dur-- ingkeying. T-he time constant of the network. comprisingthe capacitor-Grand the resistors R1, RZshouldizbe,

afirmar/7" ment according to the invention provides the equivalent of anentirely polar signal line Within practical tolerances. This is sobecause the polar signal detector device is affected only by differencesin polarity and not by differences in amplitude of the keyed signal.

The switching element S has been shown to be required to be closed whenthe voltage across the neutral input terminals 31-32 equals the voltageacross the capacitor C, and open when the capacitor voltage exceeds theinput voltage. A fast operating relay connected across the inputterminals 31-32 could be used to approximately satisfy this requirement,while a unilateral impedance element such as a diode, vacuum orotherwise, with a high back-resistance, makes an almost ideal electronicswitch. A multi-element switching tube could also be used if desirable,of course. For example, a triode tube might be used in a multiplexcircuit where a plurality of such triodes were triggered in successionor determined by the timing device of a time division multiplex system.

A practical signal repeating circuit can be made using the basicneutral-to-polar circuitry of Fig. 3 with a diode switch 61 and with asensitive polar relay 63 as an amplitude selection device as shown inFig. 6.

In this circuit, it is obvious that during spacing condition theoperating power for the polar relay 63 is supplied from the energystored in the capacitor C. In some cases this requirement for energysupply will make the desirable ratio between charging and dischargingtime constants of the shunt circuit 35 diiicult to obtain, and in suchcases the use of an electronic circuit, which requires little or noenergy from the conversion circuit, but functions on voltage diierences,is indicated. This electronic circuit may in turn drive anelectro-mechanical polar relay, or alternatively, with any required D.C.power amplification, may drive a single current relay, or the nalutilization device.

The electronic circuit may be in the fonn of the well knowndiferential-amplier circuit, or it may be of the bistablereciproconductive circuit form.

As employed herein, the term reciproconductive circuit is construed toinclude all two-tube regenerative devices in which conduction alternatesin one or the other tube in response to applied triggering potential.The term multivibrator is sometimes applied to this circuit and the termlocking circuit is sometimes applied to the bistable reciproconductivecircuit in which two triggers are required to switch from one stablestate to the other and return.

In certain instances it may be a single-ended stabilized circuit such asis commonly used in vacuum tube voltmeter circuits. Two separatestabilized single-ended ampliers may be employed in connection withpolar relays, either electro-mechanical or electronic, with one amplierconnected to one winding of the polar relay to provide bias orcorrection voltage and the other amplifier connected to the otherwinding to provide signal voltage.

The basic circuit may be used where the source twocondition signal iszero current for space and current for mark as outlined in theexplanation of the basic circuit of Fig. 3, with the resistances of theresistors R1 and R2 equal (or replaced by a center tapped singleresistor) to convert the neutral signal to a balanced polar signal andthus accurately repeat the transmitted signal without regard to theabsolute magnitude of the mar current, within, of course, the operatinglimit of the crcuit.

The basic circuit also may be used where the space condition is not zerobut of the same polarity and is proportional to the mark signal bymaking the resistances of the resistors of R1 and R2 proportional to thesum and difference ratios of mark and space signals,

and this signal will be converted to a balanced polar signal.

It may be used where the space condition is not 'zero but is of oppositepolarity and fractionally proportional to the mark signal by making theresistances of the resistors R2 and R1 proportional to the sum anddifference ratios of the mark and space signals, and this signal will beconverted to a balanced polar signal.

In any of the previous instances, if it is desired to repeat the signalwith an added characteristic distortion, or to eliminate acharacteristic distortion from the original signal by introducing anequal but opposite characteristic distortion, this may be accomplishedby changing the resistance proportions of the resistors R1 and R2. If anappropriate signal delay network, for example, the source andtransmission line impedance, is introduced in the circuit ahead of theconversion circuit, and the tap between the resistors R1 and R2 is madevariable by using a potentiometer type of resistor with or withoutseries fixed resistors, then the characteristic distortion introducedmay be varied at will and calibrated if desired.

While the basic neutral-to-polar circuit is shown as a metallic circuit,with no reference to ground, it is to be clearly understood that thecircuit may be a single-Wire and ground return circuit or may have aground connection (or ground reference connection) to either end of thepower source.

Further, the switching element S may be connected to either the groundedor ungrounded leg of the transmission line, and either polarity of thesource 18 may be grounded, provided any diode or multi-element tube usedas the switch S is properly polarized.

In the basic circuit the operating range, or the signal level variation,over which the circuit will function is limited at one extreme by theminimum sensitivity of the devices or circuits following theneutral-to-polar circuit, and at the other extreme by the maximumallowable, practicable or desirable signal available. If in practice itis desirable to provide a minimum sensitivity below which the signaloutput will assuredly be space then a minimum biasing voltagearrangement may be inserted in the neutral-to-polar conversion circuitas shown by way of example only as a battery 71 in Fig. 7. Thisarrangement will not cause any distortion to a signal that exceeds thebias voltage of the battery 71.

If a diode employing a hot cathode or other hot cathode multi-elementtube is employed as the switch and the eiects of contact potential causeundesirable output signal distortion at minimum operable signal inputlevels, the effects may be eliminated or minimized by interposing asource of corrective voltage as shown by way of example as a battery 81in Fig. 8. Compensation for both contact potential and establishment ofminimum signal bias may be combined, as shown by way of example bybatteries 81 and 71 in Fig. 19. It is to be understood, of course, thatany source of potential such as a generator, an A.C. rectifier or thelike may be substituted for the batteries shown.

In a D.-C. or on-orf single tone frequency A.C. circuit employing morethan two conditions, with each condition or combination of conditionsproviding diierent items of information, and where each condition bearsa definite proportional relationship to the maximum mark and spaceconditions, a multiplicity of the circuits according to the inventionmay be employed at the load end of the transmission line withappropriate cross connections and/ or couplings to reproduce theinformation transmitted.

In a circuit utilizing frequency shift A.C. as the'signal carrier overthe transmission line and where due to practical conditions the absolutemagnitude and/or polarity of the demodulated signal cannot: be utilizedto determine the intelligence being transmitted but where the limits ofamplitude of excursion can be established according to the invention,the neutral-to-polar conversion circuit may be adapted to definitelyinterpret the information.

-In assystememploying a.multiplicity ofusignal. .sources and/or-loadsy.withstandardized impedance I.and/o1. attenuation -characteristics,-fand f with\ yassociated `transmission-dineswhich may-shave. .differentand/ or varyinghcharacteristics, and where cross y connections y mayvVbe established between :any -pair of signal sources and Aloadsthrough-available: .transmission-lines the use` of the circuits.described allowsff-connection changes without.- the requirement oflreadjustment of sources or .loads when such .changesintroduce achangein transmissionline characteristics.

Where the basic' circuit, such as is shown lin Fig. 3, is

followed by-.a bistable..reeiproconductive or flocking circuit andreversals .are not being receivedxdur-ing idling periods, there isthedistinct possibilitythat` the-reciproconductive'=.circuit ywill betriggered to themarkingfcondition.- and 'there remain This disadvantagecan be readily'favoidedl by-rectifying the input 2signal,applying therectified signal toai.resistance-capacity.circuit of time constantlongvvithqrespect tolthe .maximum expected spacing? between .signal elementsand, .thereafter to a pulse ampliferftube'which is sofcoupled tothereciproconductive-.circuit to .restore it'to. the spacing condition.Apreferred arrangementwavoiding this. diicultyis shown in Fig. l0,wherein a pair of electrondischarge devices 83l and 8S are connected inadifterential yamplifier circuit 87. The grid'othetube 83isconnected tothe arm 91 of afpotentiometer 93fwhich serves as the'fseries connected:resistors-RL and-R2 of the .basic circuit.: A semi-conductor typerectiier 61 is shown replacing-.fthe diode previously shown. Thegermanium crystal. diode has beeniused in thiscircuit with excellentresults.

e The biasbattery j81 andv potentiometer -97 shown provide-sufiicientbiasvoltageto giveinitial unbalance of the differential ycircuit 87infthe absence 'of signal.- MWhen a signal of 1'suflicient Vstrength tocause operationof `the diode 61': appears,:the unbalancer disappearsinso far as the" response to ya-keyedwsignal isy concerned. Inithis mannersquelch action. in the absence of faxsignal is .providedy while givingproper. actiomwhen `a signal ist present without unduly-V complicatingzthe:-v circuit. A change of symmetry4 of. the .circuitswithoutdisturbingthe balance is obtainedy by providingfthe vpotentiom-eters 93land97 with identical `tapers fand' gauging: them: `for .simultaneousadjustment. S\,Direct outputds obtainedirom the'. anode of the tube 35;`Ifdesired Eau-#indirect or Ainverted :signal train may-l betakenhfromrrtheA f anode of .the :other -"tube 83. r`When derivingthcnoutputfsignal fromsthettube 83, a constant current tubelcircuitfisipreferably -used for the cathode impedance .elementninstead -f=.the.resistorf-89 where the mark-.spaceifcross-over voltage .isfclose tolthenegative -limit' of ramplitude fvariatiou.

kInFig Ill there is shown an arrangementused inlconnection :with an.'existingselectro-mechanical.multiplex receiving.v installation -where1the .signal is .transmitted as an on-off tone signal with axtone signaldem'odulatorill atftheeloadend .of the transmission line. The same:basic circuit of the inventionfollows `thexdemodulator#101sand asmoothing!lfiltervcomprising Lanfinductors103 and:- a capacitor' 105isinterposedinzthe circuit. .-Nochange lin the'theory ofoperationsisiinvolvedfprovidedthe varying attenuation characteristicsofvthe'. transmission :line :are considered'toxreact onthe'outputpower`of the demodulator inthe rsamemanner nas if the demodulatorpowerWererconstant andra. simil-arlattenuatorv werefinserted. in thetransmission line between the demodulatorvandsthe conversion' circuit.

A:potentiometer 109 in :the :input` circuit is used f to adjust. they:signal vlevel tot .obtains optimum 'resultsy from the conversioncircuit and-wthe .differential amplifier :1-11. Two outputs arefderivedA torruse in vthe multiplexV apparatus.' "The irst .isaVsignalfoutput. amplified by a .triode vacuum tuber-115`forapplic'ationtoy the messagehandling device andthe-other y'is V'aicorrection.voltagefiobtai-ned at the anode of another amplifier tube119 forLappl-icaf tion to an automatic phasing circuit in which alocally gen'cratedsignal is automatically adjusted in phase'relationship to the incoming signal. 'The amplifier tube119 acts .as anisolationdevice to prevent anyvoltage changes inthe phase adjustingcircuitry from radversely' affecting thesignal voltage" obtained 'at thesignal amplifier tube 115.

` The differential amplifier '111 is so connected that the markfspacecrossover voltage lies substantially midway of the .normal signallimits. Any large 4overshoot in signal amplitude will then have noeffect ontheoperation of the circuit and no constant currenttube-circuit is-necessary.v In'either of the arrangements shown in Figs.10 and-11, a marginal current relay may be used without any constantcurrent tube circuitry.

In order to determine `the propersetting of the levelpotentiometcr"1`09, a signal .level monitor circuit"121`is provided.'The monitor circuit 121 comprises a pair'of electron dischargestructures 12S- 124 each having a` neon indicator lamp l127; `128 in theanode-cathodev path vof theA tube. A semi-conductor Irectifier 131andiltercomprising a resistor133 anda capacitor'135 apply a'directvoltage-proportional to the peak signal level to'the grid of the signalvoltage tubefl'23.' The monitor circuit1`21 is a differential amplifierso designed thata lixed vreference voltage derived by means of resistors151 and A'152 is appliedto thegrid-of the referencettube 124. The peaksignal-'voltageapplied to' the signal tube is then compared to thereference voltage. The lcathode resistors IS7-15.9. aresochos'enthat achange of approximately 6 'db in signal-level is required for completetransfer of currenty from one of tubes '12S-124 to the other. Hence whenthe signal level is within i3 db 'of the desired level botlrneon lampsl127 and '128 will glow. 'The' cathode 'follower action of tubes"123 and124 rendersthe variation between individual neon lamps of commercialavail- Iability'of substantially no importance. Y If the'level is toohigh..only.the-neon lamp"127 will glow. Ifthe level-is too low only-vthe neon lamp'1`28 will glow. When the signal level`is-between thedesired limtsboth lamps will glow. Becaus'e'the relative brightness ofcommercially available neon. tubes iskdiscernible'to the eye, the signallevel can bereadily adjusted to lie very nearly midway between thelevels. 'I'hus the receiving station operator. can? tell at a glancewhether theproper level fof signal is being applied to the-receivingapparatus.

An example of an adaptation of the basic circuitry according to theinventionto an'electronic multiplex receiver will be found in copendingAU. S. application Serial .No-.227,344 liled May 2l, 1951,of E. R. Shenk,A. E. Canfora Vand P. `E. Volz, now yPatent No'. 2,716,158,grantedfAugust 23, l`95 5.

,In anembodiment of the invention actually constructed and 'tested alongthe lines of the arrangementlshown'in Fig. .'11, the following componentparts'values were cmployed.

' Resistors Reference No.: Value .R1 meg f 1.3 R2 meg 1.3 RB- ki1 3.9.'-109 v kil 100 A 133 kil 43 T"`151 meg l`.3

. .i152 jku l'180 1156` kil 51 -157. kil 510 158 kil 510 N159 ki l 18n.160.. meg 2.3 n.161. kil-- ...162 kil 180 163 ki1 180 f .-'165.. meg 1167 kil 270 Resistors-Continued Reference No.: Value 168 meg 2.4 169 meg1.5 171 meg 1.3 172 meg-- 2.2 173 meg-- 1.3 174 meg 2.2 175 kil 200 179kil-- 200 Capacitors Reference No.: Value C mfd-- 0.25

135 mfd 0.25

Tubes Reference No.: Type No.

110 V2 6SN7 115 1/2 6SN7 119 1/2 6SN7 127 NES 1 183 1/z 6SL7 185 1A.6SL7 Diodes Reference No.: Type No The invention claimed is:

l. In a telegraph signalling circuit arrangement having a resistivecircuit component across which a neutral mark-space signal appears, acapacitor, a rectifier element and a source of bias potential connectedin series across said resistive circuit component, and a pair ofresistance elements connected in series across said capacitor thereby toproduce a polar mark-space telegraph signal between the junction of saidresistance elements and a point intermediate the terminals of saidsource of bias potential.

2. In a telegraph signalling circuit arrangement having a resistivecircuit component across which a neutral markspace signal appears, acapacitor, a rectifier element and first and second sources of biaspotential connected in series across said resistive circuit component,and a resistor connected across said capacitor and having a variabletapping thereon, thereby to produce a polar markspace telegraph signalbetween the tapping of said resistor and the junction between saidsources of bias potential.

3. In a telegraph signalling circuit arrangement having a resistivecircuit component across which a neutral markspace signal appears, acapacitor, a rectifier and a source of bias potential connected inseries across saidA resistive circuit component, a potentiometerconnected across said capacitor, and another potentiometer connectedacross said source ot bias potential thereby to produce a polarmark-space telegraph signal between the arms of said potentiometers, anda diterential amplifier circuit including two electron discharge systemshaving anodes, grids individually connected to the arms of saidpotentiometers and cathodes connected in common, and individual anoderesistors connected to said anodes, the arms of said potentiometersbeing ganged to permit changing the symmetry of said circuitsubstantially without changing the balance thereof.

4. A circuit arrangement for converting an input signal havingexcursions of one polarity with respect to a reference value, to anoutput signal having excursions of both polarities with respect to areference value, comprising, input terminals and output terminals, adirect current impedance element connected across said input terminalsand across which said input signal appears, a

series circuit including a capacitor, a unilateral impedance device anda source of direct current potential, said series circuit beingconnected across said input terminals, a direct current voltage dividerconnected across said capacitor, a connection from an intermediate pointon said voltage divider to one of said output terminals, and aconnection from a point on said source of direct current potential tothe other of said output terminals.

5. A circuit arrangement for converting an input signal havingexcursions of one polarity with respect to a reference value, to anoutput signal having excursions of both polarities with respect to areference value, comprising, input terminals and output terminals, adirect current impedance element connected across said input terminalsand across which said input signal appears, a series circuit including acapacitor, a unilateral impedance device and a source of direct currentpotential, said series circuit being connected across said inputterminals, a direct current voltage divider connected across saidcapacitor, a connection from an intermediate point on said voltagedivider to one of said output terminals, and a connection from anintermediate point on said source of direct current potential to theother of said output terminals.

6. A circuit arrangement for converting an input signal havingexcursions of one polarity with respect to a reference value, to anoutput signal having excursions of both polarities with respect to areference value, comprising, input terminals and output terminals, adirect current impedance element connected across said input terminalsand across which said input signal appears, a series circuit including acapacitor, a unilateral impedance device and a source of direct currentpotential, said series circuit being connected across said inputterminals, a direct current voltage divider connected across saidcapacitor, a connection from an intermediate point on said voltagedivider to one of said output terminals, and a connection from thejunction between said unilateral impedance device and said source of'direct current potential to the other of said output terminals.

7. A circuit arrangement for converting an input signal havingexcursions of one polarity with respect to a reference value, to anoutput signal having excursions of both polarities with respect to areference value, comprising, input terminals and output terminals, adirect current impedance element connected across said input terminalsand across which said input signal appears, a series circuit including acapacitor, a unilateral impedance device and a source of direct currentpotential, said series circuit being connected across said inputterminals, a direct current voltage `divider connected across saidcapacitor, a connection from an intermediate point on said voltagedivider to one of said output terminals, and a connection from the endof said source of direct current potential connected to one of saidinput terminals to the other of said output terminals.

8. In a telegraph signalling circuit arrangement having a resistivecircuit component across which a neutral mark-space signal appears, acapacitor, a rectifier and a source of bias potential connected inseries across said resistive circuit component, a potentiometerconnected across said capacitor, and another potentiometer connectedacross said source of bias potential, and output terminals connectedrespectively to said potentiometers, whereby to provide a polarmark-space telegraph signal at said output terminals.

References Cited in the le of this patent UNITED STATES PATENTS2,424,961 Bancroft et al Aug. 5, 1947 2,513,910 Bliss July 4, 1950FOREIGN PATENTS 691,625 Germany June 1, 1940

